1. Field of the Invention
The present invention relates to a magnetic storage control apparatus, a magnetic storage control method, and a magnetic storage apparatus that corrects a recording clock.
2. Description of the Related Art
A conventional hard disk drive uses a recording clock (fixed clock) having a previously-determined frequency to recording data in a medium. However, a slight variation in the linear velocity occurs in a track where recording is in progress due to influence of decentering (displacement between the central axis of a medium and central axis of a spindle). Therefore, in the case where recording is performed using the fixed clock, the frequency of data recorded in the medium does not become constant (in other words, recording bit length does not become constant). Thus, it is necessary to ensure an extra data area (buffer) in consideration of the displacement in the frequency. As a result, format efficiency (recording capacity) becomes low.
In order to correct the displacement in the frequency occurring due to influence of such decentering, there has been proposed an apparatus that measures the errors in the frequency and phase between respective servo sectors based on servo information and corrects the frequency based on the measured errors using a clock interpolator (refer to, e.g., Patent Document 1: U.S. Patent Application No. 2004/0201913).
When the error is fed back so as to correct the frequency and phase of the recording clock with respect to the decentering, a tracking error (group delay) occurs.
Further, when a method using a recording clock of a frequency that has previously determined for each servo sector is employed, the amount of displacement in the frequency becomes large at the latter part of the servo sector.
As described above, even if the correction is applied, it is impossible to eliminate the need to ensure a buffer due to occurrence of the displacement in the frequency of the recording clock, with the result that format efficiency cannot be improved.